What is the test for a judge to order that counsel's statements are not evidence?

A trial judge must avoid the appearance of partiality. Id. at 552. However, a judge is not " 'expected to sit mute and impassive, speaking only to rule on motions or objections.' " Id. at 552-53 (quoting United States v. Eldred, 588 F.2d 746, 749 (9th Cir.1978)). An instruction that counsel's statements are not evidence is proper and must be timely in order to neutralize prejudice. United States v. Tootick, 952 F.2d 1078, 1085 (9th Cir.1991) ("The judge must actively supervise the trial, and if necessary, reiterate instructions in the wake of prejudicial events.").